1. Field of the Invention
The present invention relates to a lane departure warning device, for example, a lane departure warning device for detecting positions of traffic marking lines of a lane where an own vehicle is traveling by using an image pickup device (on-board camera), predicting a possibility of departure of the own vehicle from the lane, and providing a warning if the predicted possibility of departure is high.
2. Background Art
There have been suggested various techniques of recognizing objects (such as vehicles and pedestrians) or traffic markings and signs (road paintings such as a traffic marking line, and traffic signs such as a Stop sign) in an image of surroundings of the own vehicle picked up by an on-board camera of the own vehicle. For example, if traffic marking lines such as white lines painted on a road and Botts' dots can be detected by an on-board camera so that a vehicle position in the lane, that is, a relative position of the vehicle to the traffic marking lines can be found, it is possible to predict how high the possibility of the vehicle's departure from the lane is, and if the possibility of the departure is high, a warning is provided for a driver or steering and braking are controlled, thereby preventing the departure from the lane in advance or reducing the degree of such departure.
Examples of the above mentioned systems for providing a warning when there is a high possibility that a vehicle is likely to depart from a lane are lane departure warning systems (LDWS) standardized by JIS D0804 of JIS (Japan Industrial Standard) and by ISO/DIS 17361 of ISO (International Organization for Standardization).
As a technique to realize such systems, JP Patent Publication (Kokai) No. 2010-191893A discloses a device that recognizes traffic marking lines in the vicinity of a vehicle based on a picked up image, calculates a distance from each end of the own vehicle to each traffic marking line, and provides a warning if the distance is less than a predetermined value, or predicts TLC (Time to Line Crossing) that is time required for the own vehicle to depart from a traveling lane and if this predicted TLC is less than a predetermined time.
Unfortunately, the lane departure warning device disclosed in JP Patent Publication (Kokai) No. 2010-191893A sometimes provides lane departure warning when a value of the TLC becomes less than the predetermined time even though the vehicle about to depart from the lane is avoiding the lane departure by a quick steering immediately before the lane departure (before the distance to the traffic marking line becomes less than a predetermined value). This is because calculation of image recognition is usually delayed from a vehicle behavior, and the device sometimes provides a warning although a driver is intentionally avoiding the lane departure, and the driver may feel it irritated. Hence, such a warning is categorized into a false warning. A false warning is most likely to occur in a device configured to pick up an image behind a vehicle and provide a lane departure warning using the picked up image.